New API for flushing to the database and invalidating the cache with #87527. New methods have been added to odoo.models.Model and odoo.api.Environment, and are less confusing about what is actually done in each case. See the section SQL Execution.
Odoo Online version 15.2
Specific index types on fields: With #83274 and #83015, developers can now define what type of indexes can be used on fields by PostgreSQL. See the index property of odoo.fields.Field.